Adipic acid, which is a raw material of 66-nylon, and ε-caprolactam, which is a raw material of 6-nylon, are manufactured on a worldwide scale in amounts of 2.2 million tons and 3.7 million tons per year respectively.
Adipic acid is obtained industrially by oxidizing cyclohexanone, cyclohexanol, or a mixture thereof with nitric acid. ε-caprolactam, on the other hand, is obtained through a rearrangement reaction of cyclohexanone oxime that has been obtained by converting cyclohexanone into the oxime. Moreover, KA oil, which contains cyclohexanone and cyclohexanol is manufactured through a cyclohexane oxidation process or a phenol hydrogenation process, and it has been reported that the amount of KA oil produced per year is 5 million tons (Sekiyu Kagaku Purosesu (“Petrochemical Processes”), edited by the Japan Petroleum Institute, Kodansha, pages 144-148 (2001)).
However, out of these processes, with the cyclohexane oxidation process, approximately 20% of higher oxides are produced, and the handling thereof is problematic. On the other hand, with the phenol hydrogenation process, KA oil has been obtained through a vapor phase method using a supported palladium catalyst by reacting a phenol or the like in a temperature range of 130 to 180° C. so as to hydrogenate the benzene ring of the phenol (N. Mahata and V. Vishwanathan, Journal of Catalysis, 196, 262-270 (2000)). This method of hydrogenating phenol has the drawback that the reaction temperature is high, and hence the catalyst is prone to being deactivated through accumulation of carbonaceous matter on the surface thereof during the reaction; making the reaction proceed at a lower temperature has thus become an issue. Moreover, there has been proposed a method of synthesizing 3-methylcyclohexanone and 3-methylcyclohexanol from meta-cresol through hydrogenation using carbon dioxide and a 5% palladium catalyst under reaction conditions of 250 to 400° C. and a (CO2+H2) pressure of 120 bar (Published Japanese Translation of PCT Application No. 2000-508653) However, with this type of hydrogenation method, drawbacks have been observed in that deoxygenation and functional group breakaway occur so as to produce unwanted byproducts such as methylcyclohexane and toluene. Moreover, the supported metal of the catalyst used in such a hydrogenation method is limited to palladium, and hence it has been difficult to reduce the reaction temperature, or improve properties such as the activity and selectivity; there have thus been calls for the development of a new highly active metal catalyst.